In winding coils on motor armatures, it is necessary to keep the coil wire taut throughout the coil winding operation in order to ensure a necessary density of the coil wire in each coil. Conventionally, a self-adjusting brake was used to apply an appropriate tension to the coil wire. According to such a brake, when there is an increase in the tension of the wire, this causes an increase in the deflection of the spring member which in turn causes a reduction in the braking force applied to an upstream end of the coil wire, thereby keeping the tension of the wire substantially at a constant level. However, such a brake can offer a limited precision in controlling wire tension, and is often inadequate for modern high speed motor coil winding machines.
Furthermore, in winding coils around core teeth of an armature, it is necessary to hook the coil wire around risers between succeeding coil winding steps and terminal ends of the coil wires must be severed, and these additional steps in motor coil winding operations require different coil wire tensions, but conventional brakes are totally incapable of varying the tension of the coil wire, and imposed a severe restriction in obtaining high quality coils and speeding up the coil winding operation.